Exhumation of crustal slivers in a subduction mélange in the Betic Cordillera, SE Spain

Abstract

With the recent recognition of Miocene subduction ages in the lower nappes of the Betic Cordillera, its tectonometamorphic evolution has become a point of discussion again. Neither of the two current models fully explains the metamorphic events found within the rocks of this domain, especially in the upper part of the downgoing plate. The metamorphic evolution and contrast between nappes are reassessed here for the eastern Sierra de los Filabres to obtain a clearer view on the Spanish Betics. Two units can be distinguished between the subducted and later exhumed Iberian plate, and the interface with the overriding plate. The lower unit is a mafic slice intercalated with metasediments, which represents part of a rifted margin metamorphosed under medium pressure amphibolite facies conditions. The upper unit is a mélange of various lithologies, mostly serpentinite bodies in the lower part and metasedimentary and granitic blocks in the upper part. High-pressure P-T paths have been derived from these units of up to 1.6-1.8 GPa and with minor retrogression, however they do show contrasting geothermal gradients and peak conditions. The mixing of crustal blocks and serpentinite bodies in the upper unit suggests that it is an accretionary complex, formed by underplating as crustal blocks detached and became exhumed along the subduction channel. This explains the metamorphic contrasts and exemplifies the exhumation of large crustal blocks in a subduction setting. It also supports the slab rollback hypothesis for the Betic Cordillera. This project has received funding from the ERC (grant agreement No 714936) to M. Alvaro

Full text

Goldschmidt2018 Abstract
Exhumation of crustal slivers in a
subduction mélange in the Betic
Cordillera, SE Spain
H.W. VAN SCHROJENSTEIN LANTMAN1,2*, L.M.
KRIEGSMAN2,3 & H.L.M. VAN ROERMUND 2
1Department of Earth and Environmental sciences, University of
Pavia, Italy (* correspondence:
hugo.vanschrojenste01@universitadipavia.it)
2Department of Earth Siences, Utrecht University, Netherlands
3Naturalis Biodiversity Center, Leiden, Netherlands
With the recent recognition of Miocene subduction ages in the
lower nappes of the Betic Cordillera, its tectonometamorphic
evolution has become a point of discussion again. Neither of the
two current models fully explains the metamorphic events found
within the rocks of this domain, especially in the upper part of
the downgoing plate. The metamorphic evolution and contrast
between nappes are reassessed here for the eastern Sierra de los
Filabres to obtain a clearer view on the Spanish Betics.
Two units can be distinguished between the subducted and later
exhumed Iberian plate, and the interface with the overriding
plate. The lower unit is a mafic slice intercalated with
metasediments, which represents part of a rifted margin
metamorphosed under medium pressure amphibolite facies
conditions. The upper unit is a mélange of various lithologies,
mostly serpentinite bodies in the lower part and metasedimentary
and granitic blocks in the upper part. High-pressure P-T paths
have been derived from these units of up to 1.6-1.8 GPa and with
minor retrogression, however they do show contrasting
geothermal gradients and peak conditions.
The mixing of crustal blocks and serpentinite bodies in the upper
unit suggests that it is an accretionary complex, formed by
underplating as crustal blocks detached and became exhumed
along the subduction channel. This explains the metamorphic
contrasts and exemplifies the exhumation of large crustal blocks
in a subduction setting. It also supports the slab rollback
hypothesis for the Betic Cordillera.
This project has received funding from the ERC (grant agreement
No 714936) to M. Alvaro